Method for producing a ceramic covered magnetometer core



METHOD FOR PRODUCING A CERAMIC COVERED MAGNETOME'IER CORE Filed Dec. 22. 1966 FIG. 3

mvsmox Joel H. Gregowski A RNEY United States Patent US. Cl. 29-602 2 Claims ABSTRACT OF THE DISCLOSURE The invention is a method for improving the permeability of a ferromagnetic core and protecting it from flexing by annealing the core material and cementing it inside a ceramic tube.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to magnetically saturable cores, and more particularly to core assemblies and a method of annealing said cores.

In the preparation of magnetic cores certain heat treating steps are necessary to provide optimum performance particularly when said cores are to be used in sensitive devices such as magnetometers for measuring weak magnetic fields, such for example as the earths magnetic field. In the core materials used in such sensitive devices, one of the problems which decreases the accuracy and causes malperformance in operation is that of residual magnetism in the core material. By annealing the core material, residual magnetism is reduced and the permeability of the core material is improved. However in small diameter cores having dimensions in the order of a small wire an additional problem is posed in the nature of keeping the core from being bent or flexed after the annealing process has taken place. Such bending or flexing caused by handling of the cores, may destroy the results of the annealing process.

It is an object of this invention to provide an annealed core for use in the sensing element of a magnetometer.

It is another object of this invention to provide a core structure for a magnetometer which is free of residual magnetism.

It is a further object of this invention to improve the reliability of a magnetometer.

It is yet another object of this invention to provide a method of producing suitable cores for magnetometers.

It is yet a further object of this invention to provide means for reducing the possibility of damage to magnetic cores after the cores have been annealed.

A still further object of this invention is to provide a method of preparing magnetic cores in which the proportion of defective cores caused by physical deformation after annealing is reduced.

According to the present invention, the foregoing and other objects are attained by a magnetic core fabricated by placing lengths of the core material within rigid, insulating tubes such as ceramic tubes before heat treatment and permanently retaining the tube and core elements together to operate as a portion of a sensing element of a magnetometer.

A more complete appreciation of the invention and many of its attendant advantages will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

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FIG. 1 illustrates a cross-sectional view of the core assembly of this invention;

FIG. 2 illustrates a method of bonding the core and the ceramic tubes; and

FIG. 3 shows the core assembly placed within a coil.

Referring to FIG. 1, a core assembly 11 is shown in which a ferromagnetic core 13 is disposed within a ceramic tube 15. The core is shown placed even with one end of the ceramic tube 15. The core material may have the following composition:

Percent Nickel 79 Molybdenum 4 Manganese 0.5 Silicon 0.15 Carbon 0.05 Iron 16.3

INITIAL ASSEMBLY The core 13, which must be clean and free of burrs and bends, is carefully slipped into the precleaned ceramic tube 15. The core is positioned so that it is even with one end of the tube. The ceramic tube and core assembly must be maintained in the horizontal position at all times until the core is later cemented in place in order to prevent slippage.

After the initial assembly, the tube and core sets are cleaned with a solvent such as acetone.

ANNEALI-NG The following steps are taken in annealing the core:

(1) Introduce electrolytic dry hydrogen into the furnace chamber at a flow rate of to cubic inches per minute.

(2) Raise furnace temperature to 1350 and hold.

(3) Introduce wet hydrogen gas for three (3) hours.

(4) Re-introduce dry hydrogen gas and continue to hold the temperature at 1350 F. for an additional three (3) hours.

(5) Raise the furnace temperature to 2300 F. and hold for four (4) hours.

(6) Allow furnace to cool to room temperature.

(7) Raise furnace temperature to 1350 and hold for four (4) hours.

(8) Allow furnace to cool to room temperature at a controlled rate of one (1) degree Fahrenheit per minute.

Referring now to FIG. 2 of the drawings a core and tube set 11 is shown in which ceramic tube 15 is connected at one end to a tube 17 which leads to a source of vacum such as vacuum pump 19. The other end of the ceramic tube is immersed in a container 21 containing rubber cement 23. A pin 25 may be placed in ceramic tube 15 to prevent core 13 from being removed by the vacuum applied during the cementing operation. The cement 23 is shown in the tube as rising to level 24 during the cementing. The cement will fill the entire length of the tube however before the vacuum is removed.

This apparatus is used for a portion of the final assembly and reheating process described hereafter.

FINAL ASSEMBLY AND REHEATING (1) Insert one end of tube into a section of flexible hose which is connected to the vacuum pump.

(2) Apply a vacuum (about 20 mm. Hg) to the tube and core assembly.

(3) Place the other end of the ceramic tube just below the surface of a solution of thinned rubber cement. The rubber cement is then drawn up and around the core material by the vacuum pump.

(4) Remove the vacuum and clean the surfaces of the ceramic tube.

(5) Place tube and core assembly in an oven at a temperature at 150 and allow to'remain for four (4) hours.

In FIG. 3 of the drawings, a core and tube assembly 11 is shown disposed within a spool 31 of a coil or sensing element 33. In addition to the core and tube assembly 11 and the spool 31, the'coil or sensing element may include one or more windings 35.

The furnace used in the above heat treating may be a hydrogen anneal furnace as, for example, a Lindberg type CF-l. The vacuum pump used may be any vacuum pump which is capable of producing a vacuum of 20 millimeters of mercury. The core 13 of FIG. 1 may have a length of 1.5 inches and a diameter of 0.01 inch with a a tolerance of :.001 inch. The ceramic tube 15 may have a length of 2 inches, an outer diameter of 0.40 inch and an inner diameter of 0.012 inch. The, inner diameter tolerance being +.'005 inch and .000 inch.

Obviously many modifications and variations are possible in the light of the above teachings. It is therefore to be understood that within the light of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A method of preparing a linearly disposed ferromagnetic core comprising the steps of,

inserting a linearly disposed core within a rigid insulating tube,

placing said core and tube in a furnace and heating to amend said core,

cooling said core and tube at a controlled rate,

cementing said core and tube together,

placing said core and tubing into an oven and reheat- 2. A method of preparing a linearly disposed ferromagnetic core as in claim 1 in which said cementing includes the steps of placing one end of said tube in a liquid solution of rubber cement and applying a vacuum to the other end of said tube.

References Cited UNITED STATES PATENTS 1,924,311 8/1933 Frey. 2,606,849 8/ 1952 Dantsizen. 2,820,720 1/ 1958 Ivevsen. 3,419,958 1/ 1969 Obenschain.

REUBEN EPSTEIN, Primary Examiner US. Cl. X.R. 

